Prosthetic home intervention induces cortical plasticity in paediatrics with congenital limb reduction

Abstract Paediatrics with congenital upper-limb reduction deficiency often face difficulties with normal development such as motor skills, needing assistance with daily activities such as self-care limitations with certain movements, sports, or activities. The purpose of this non-randomized longitudinal controlled trial was to assess, using intent-to-treat analysis, the effects of an 8-week home intervention of prosthetic use on the sensorimotor cortex in paediatrics with congenital upper-limb reduction deficiency. A paediatric population with congenital upper-limb reduction deficiency (n = 14) who were aged 6–18 years and who had a 20° or greater range of motion in the appropriate joint of the affected arm to move the body-powered prosthesis were enrolled. An age- and sex-matched control group (n = 14) was also enrolled. Participants were non-randomized and fitted with a custom low-cost 3D printed prosthesis and participated in 8 weeks of prosthetic use training at home. Control participants utilized a prosthetic simulator. The home intervention incorporated daily use training and exercises utilizing the prosthesis in direct use and assistive tasks explained by the researchers. After the home intervention, both groups displayed significant improvements in gross manual dexterity. During prosthetic use with the affected limb, significant increases in oxygenated hemodynamic responses were only displayed in the left premotor cortex of the upper-limb reduction deficiency group. The novel findings of this non-randomized longitudinal controlled trial suggest that the intervention may have improved the functional role of the left hemisphere which translated to the improvement of learning direction during adaptation to visuomotor control. The prosthetic home intervention was assumed to provide closed-loop training which could provide a direct benefit to the motor development of paediatrics with upper-limb reduction deficiency.


Introduction
The Centers for Disease Control and Prevention (CDC) reports that approximately 4 out of every 10 000 babies are born with upper-limb reductions every year in the United States. 1,2Other parts of the world report this number from 3.4 to 5.3 of 10 000 children. 3 However, many cases are unreported due to the lack of a mandatory reporting system of birth defects and amputations at a young age.In order to restore function in paediatrics with upper-limb reduction deficiencies (ULRD), the main treatment is the use of a prosthetic device. 1 However, the main barrier to treatment is the cost of providing a functional prosthesis, which ranges from $4000 to $10 000 for a body-powered prosthesis and $25 000 to $75 000 for an electronically driven prosthesis. 4,5][11] While the factors for rejection are exclusive to the design of the prosthesis, previous literature suggest that the involvement of the specific neuronal control mechanisms that limit the functional of these devices. 9,10,12Thus, there is a significant knowledge gap about the neural mechanism underlying the high rejection rate of upper limb prostheses in a paediatric population. 9Our previous studies have focused on this knowledge gap to identify the muscle coactivation, 13 functional changes, 14 and brain lateralization 15 in paediatrics with ULRD as they utilize 3D printed, body-powered prostheses.
Further evidence has now established that the two cerebral hemispheres show a considerable degree of motor lateralization, in which the left and right hemispheres are specialized for various aspects of motor control. 168][19][20] We have additionally conducted preliminary data in a case study which indicated that drastic changes in hemodynamic responses occurred after prosthesis use training. 21Thus, the purpose of this study was to expand this case study to a larger, longitudinal clinical trial to increase the impact of these results.We hypothesize that 8 weeks of the prosthesis use home intervention will produce robust changes to the sensorimotor cortex of paediatrics with ULRD.Our secondary hypothesis is that there will be a nonsignificant difference in gross manual dexterity between device use (i.e.prosthetic and prosthetic simulator) and intact hand use (i.e.non-affected and dominant hand) before the onset of the home intervention.

Materials and methods
All parents and their children were informed about the study and parents signed a parental consent.An assent was explained to the paediatric and signed by the children and their parents.In the state of Nebraska, the age of consent to sign a document is 19 years of age, so a parent's signature was needed for the entire paediatric population in this study.Thus, the paediatric population will hereby be referred to as 'participants.' Consent and assent were obtained according to the Declaration of Helsinki.Detailed safety guidelines were given to the parents regarding the use and care of the prosthesis.The study was approved by the University of Nebraska at Omaha Institutional Review Board.The trial was prospectively registered at ClinicalTrials.gov(NCT04110730).This trial followed the Transparent Reporting of Evaluations with Nonrandomized Designs (TREND) reporting guidelines (Fig. 1).

Outcomes
Measurements were performed before and after an 8-week home intervention using a wrist-driven 3D printed transitional hand prosthesis (Fig. 2).Oxygenated haemoglobin as calculated from functional near-infrared spectroscopy (fNIRS) data recordings were indirect indicators of cortical activity during a gross manual dexterity task.Functionality was assessed via performance score on the box and blocks test.

Participants
Participants were recruited from the community via outreach to clinicians and support groups, existing databases and health record systems.Inclusion criteria for all participants included a paediatric population with congenital ULRD.Wrist and elbow range of motion of the affected limb had to be greater than 20° in order to activate the body-powered prosthesis.Exclusion criteria included upper extremity injury within the past month and any medical conditions that would contraindicate the use of the transitional prosthesis, such as skin abrasions and musculoskeletal injuries.
Fourteen participants (Table 1) with congenital upper-limb deficiencies participated in this study and were fitted with a wrist-or elbow-driven 3D printed prosthesis (Fig. 2A).A sex-and age-matched control group were recruited to participate in this study and were fitted with a matched wristor elbow-driven 3D printed prosthetic simulator on their non-dominant hand (Fig. 2A).The prosthetic fitting was performed by a certified prosthetic and orthotic professional.Data collections and prosthetic fitting occurred in the Biomechanics Research Building at the University of Nebraska at Omaha from January 2020 to December 2022.This study was powered to detect a between-group difference of performance in a gross manual dexterity test and brain lateralization 15 using the free to use software G*Power.Covariant parameters and ULRD group changes were identified from a previous case study. 21Calculations indicted a total target sample size of 40.Considering the effect size from preliminary data and to account for a 10% drop-out rate, a total sample of 40 subjects was determined to provide 80% power to detect a true standardized effect size.These calculations were made before any analysis of outcome data.

Prosthesis home intervention
After screening and baseline testing, eligible participants participated in 8 weeks of prosthetic use training in the comfort of their own homes.The home intervention protocol followed previously reported procedures assessing paediatric functional motor skills utilizing a prosthesis, 22  two training sessions per week lasting for approximately 1 h for 8 weeks over video conference with the research personnel who were blinded to the aim of the study.
During the prosthesis home intervention, participants completed activities to assess functional completion of activities of daily living with the prosthesis under the direction of the research personnel.All activities were executed by telling the participant, 'Ready, Set, Go' and ending with 'Stop' with the exception of the drawing activity.The activities included Block Building, Utensils, Paper Activities, Ball Play, Tray Carry and Bike Circuit. 22he Utensils, Paper Activity, Ball Play and Tray Carry were considered training tasks, as they occurred during each training session.Utensils consisted of using the participant's unaffected extremity and the prosthetic appendage to make four cuts with a fork and knife while utilizing a universal cuff to grasp the utensil in the prosthesis.Paper Activities consisted of several parts, stabilizing a piece of paper while the participant draws on it, folding the piece of paper, stabilizing a tape dispenser with the prosthesis to tear three pieces of tape, and holding the paper with the prosthesis while the able hand uses scissors to make three cuts.During Ball Play, the participant must use the prosthesis to pick up a ball from the ground and either underhand or overhand toss it to a partner three times in a row.During Tray Carry, participants walked in a Figure 8 formation around two toys placed approximately 5 ft apart while balancing a tray loaded with two cups between their prostheses and unaffected upper extremity.
The Block Building and Bike Circuit activities were considered non-training tasks and only completed during the first and last weeks of the prosthesis home intervention to assess the pre-and post-intervention abilities.The Block Building activities included two trials of a series of six different Block Building activities for each hand separated by 30 s of rest (a total of 18 block building activities per hand).Specifically, the participant was instructed to perform three trials of the following building block activities: 4-block train, 3-cube bridge, 4-block wall, 3-block tower, 6-block steps and 6-block pyramid.The Bike Circuit required participants to either ride a bike or walk a bike in a Figure 8 around two stationary objects approximately 5 ft apart to demonstrate independent bilateral forearm activation in order to turn the bike with the able appendage and the prosthesis.

Printed body-driven prosthesis characteristics
The Cyborg Beast 2 (Fig. 2A) was utilized in this study and manufactured in the Additive Manufacturing Laboratory located in the Biomechanics Research Building at the University of Nebraska at Omaha.14,15

Gross manual dexterity test
The Box and Block Test is a measure of unilateral gross dexterity (Fig. 2B). 23,24During the task, the participants were instructed to move one block at a time, transporting it over the partition and dropping it in the opposite compartment.The participants were instructed to move as many blocks as possible within a 60 s period.This was followed by 60 s of rest.Three trials were performed for each limb condition (affected using the prosthetic and non-affected for ULRD group; nondominant using the simulator and dominant for control group).The number of blocks moved was recorded for each trial.

Hemodynamic response measurements
Hemodynamic response data were collected using a continuous wave fNIRS system (NIRSport 2, NIRx Medical Technologies, LLC, Berlin, Germany) and Aurora fNIRS-NIRSport 2 Acquisition Software (version 2020.7.2.0).Data were sampled at 8 Hz operating at 760 and 850 nm wavelengths.fNIRS data were collected during the Box and Blocks Test for each limb condition performing the task.The Aurora fNIRS software allowed for an automated signal optimization algorithm to be used during signal calibration which ensured and served as an early-stage signal quality check before data were recorded.Eight sources and eight detectors were placed in a cap fitted to each participant's head circumference (Fig. 2C).The cap was positioned on the head following the 10-20 international system and the probes were placed according to a standardized montage available through the NIRx support portal (NIRSite Montage Motor 8 × 8). 25 The fNIRS channels covered the area around the C3 and C4 landmarks which have been shown to detect motor activity that drives hand and arm movement. 26

Statistical analysis
The AnalyzIR Toolbox 27 was used to analyze the fNIRS data.
The raw fNIRS signals were first converted into changes in optical density data by taking the logarithm of the signal.Optical density data were then filtered with a fourth order bandpass filter (high pass = 0.01 Hz; low pass = 0.2 Hz) in order to remove for any physiological noise. 28The oxygenated-hemoglobin (HbO) concentrations were then obtained using the modified Beer-Lambert law.The hemodynamic response function was then estimated by a general linear model (GLM) approach that uses autoregressive iterative reweighted least squares, which corrected for motion artifacts. 29The response was modelled using the Canonical temporal basis function with a peak time of 4 s.Beta values (i.e.changes in HbO) were calculated during the GLM analysis and represent the weighted responses of the individual channels during the task compared to baseline levels.For whole-brain analysis, Student's t-statistic estimates and Benjamini-Hochberg false-discovery rate corrected P-values (q-values) were also calculated, which addresses the problem of evaluated type 1 error due to multiple comparisons.A significance level of q < 0.05 was used in heatmaps of T-scores plotted in 10-20 format.For analysis of the Box and Blocks Test, a two-way repeated measures ANOVA [2 × 4; group (ULRD versus Control) × hand (affected limb using prosthesis versus non-dominant limb using simulator versus non-affected limb versus dominant limb)] was used to test group versus hand interactions.A Student's t-statistic was utilized to determine between group differences.A P-value of less than 0.05 was considered statistically significant for all comparisons.

Recruitment and retention
We consented and screened a total of 40 participants who were eligible for this non-randomized controlled trial.
However, a total of 28 participants were included in the final data analysis presented in this manuscript, and the demographics are displayed in Table 1.A total of 12 participants were excluded from the final analysis due to the following reasons: (1) participants (n = 1) did not complete the full 8 weeks of training; (2) participants (n = 7) withdrew from a data collection session, baseline or follow-up, or the data set was considered incomplete; (3) the inclusion criteria of an age-and sex-matched control was not met (n = 4).

Box and Blocks Test
There was a significant interaction between-groups for gross manual dexterity performance, F(1,7) = 134.25,P < 0.0001.Post-hoc analyses revealed that during the baseline assessment the affected limb using the prosthesis of the ULRD group performed similarly (P = 0.9668) to the nondominant limb using the simulator of the Control group.Likewise, during baseline assessment, the non-affected limb of the ULRD group performed similarly to the dominant limb of the Control group (P = 0.6098).
After the completion of the home intervention, these between-group comparisons did not change.During the post-assessment, the affected limb using the prosthesis of the ULRD group performed similarly (P = 0.9298) to the non-dominant limb using the simulator of the Control group.Likewise, the non-affected limb of the ULRD group performed similarly to the dominant limb of the Control group (P = 0.1249) during the post-assessment.
In agreement with our hypothesis, there was a significant improvement due to the home intervention.After intervention (Table 2), there was a significant improvement in gross manual dexterity within the ULRD group of the affected limb using the prosthesis (P = 0.0264) and the non-affected limb (P = 0.0003).This significant improvement in gross manual dexterity was also seen within the TD group using the simulator (P = 0.0329) and the dominant limb (P = 0.0111).

Areas of cortical activation
Cortical activation maps for each group are presented in Fig. 3. Channels that produced a statistical significance of cortical activation surviving multiple comparisons correction (q < 0.05) and a positive T-score (T-score > 0.0) were considered to contain significant cortical activation and are depicted in solid lines.Before the home intervention, significant cortical activation was produced in all groups and conditions except in the non-dominant limb using the simulator of the Control group.When active, various channels over the left premotor cortex were always significantly active.However, the channels over the right premotor cortex were only significantly active when intact limbs performed the Box and Blocks test.Additionally, various channels over the primary motor cortex were significantly active in both hemispheres within each group, except the aforementioned Control group.Lastly, similar significant activities were produced in the sensory cortex, except in the non-affected limb of the ULRD group.
After the home intervention, a greater number of channels were significantly active.Widespread changes were especially seen in the affected limb using the prosthesis of the ULRD group.Most channels became significantly active with the exception of one channel (S5, D7) located in the right primary motor cortex.

Effects of intervention on oxygenated hemodynamic responses
Comparisons of ΔHbO responses for each group before and after intervention are presented in Fig. 4. The home intervention produced a significant increase in the ΔHbO recorded from one channel (S1, D1) located in the left premotor cortex.This significant increase was only seen in the affected limb using the prosthesis of the ULRD group (q = 0.0042).There were no significant changes in ΔHbO in the nonaffected limb of the ULRD group nor in either limb of the Control group (q > 0.05).

Adverse events
There were no serious adverse events related to study procedures to report.

Discussion
The novel finding of this longitudinal clinical trial partially agrees with our hypothesis that the home intervention would cause robust changes to the sensorimotor cortex (Fig. 3).However, the changes seen after 8 weeks of prosthesis home intervention were only restricted to the left premotor cortex of the ULRD group when using the prosthesis with the affected limb (Fig. 4).Secondary findings agree with the hypothesis indicating a non-significant difference in gross manual dexterity between prosthetic and prosthetic simulator groups and between the non-affected and dominant hand groups before the onset of the home intervention (Table 2).

Gross manual dexterity in terms of handedness
The results of the Box and Blocks Test were in agreement with our previous studies that also showed no significant difference in gross manual dexterity between the ULRD group using the prosthesis and typically developing Control group using the simulator. 15However, the nonsignificant difference in gross manual dexterity between the ULRD's non-affected limb and Control's dominant limb disagrees with previously reported performances that showed the ULRD group performed significantly lower than the Control group during the Box and Blocks Test. 15ainburg et al. have indicated that the dominant-arm system controls movement extent largely through planning mechanisms that specify 'open-loop' control, while the non-dominant arm system does so largely through feedback mechanisms or 'closed-loop' control. 30,31In the context of this study, the affected limb of the ULRD group was assumed to be non-dominant limb; however, the handedness of the affected limb was not utilized as a covariant.After intervention, both limbs in each group performed significantly better during the Box and Blocks Test (Table 2).Since the intervention improved performance of both limbs within the ULRD group, these results suggest that the intervention provided a profound benefit on both the planning (openloop) as well as the feedback (closed-loop) systems of the ULRD group regardless of the handedness of the affected limb.

Interpretation and generalization of induced cortical plasticity
The baseline activation maps produced during the Box and Blocks Test in the current study (Fig. 3) agree with our previous report where it was shown that ULRD children, unlike a typically developing Control group, showed significant activation in both hemispheres. 155][36] However, it has been suggested that children may lack lateralization in the early stages. 37More importantly, this bi-lateral response has also been shown in healthy adults during unilateral finger movement 38,39 and unilateral arm movements, [40][41][42] which agree with the activation maps of the Control group using the dominant limb.After intervention, a greater number of channels became active in the ULRD group.This may suggest that the intervention produced large-scale inter-network communication across hand-selective areas, which has been reported in amputees utilizing a prosthesis daily. 43Thus, it is reasonable to suggest if the child uses the prosthesis extensively, it would facilitate the representation of the arterial limb on areas of the motor cortex normally devoted to the missing limb thus facilitating prosthesis acceptance and embodiment. 10,12,15ue to these results showing bi-lateral activation during unilateral limb movements, it has been suggested that there is a functional role for each hemisphere. 44For motor function, it has been suggested that the left hemisphere controls predicting and accounting for limb dynamics while the right hemisphere controls stabilizing limb position through impedance control mechanisms. 16,45For example, it has been shown in right handed individuals that left, dominant hemisphere damage produced deficits in intersegmental coordination and in direction learning during adaptation to visuomotor rotation, whereas right, non-dominant hemisphere damage produced deficits in final position accuracy and position adaptation. 17,18,20ccording to the neuronal group selection theory, the ULRD population may lack representation of the missing part of the limb in the cerebral cortex. 10,12,15,46Thus, one could speculate that the ULRD group, with a congenital as opposed to acquired limb reduction, would show most control deficits related to the affected hemisphere.Since intersegmental coordination and final position accuracy and adaptation were not specifically measured in this study, we will focus on the increase in HbO response of the left premotor cortex (Fig. 4) due to the intervention.This result suggests that the intervention may have improved the functional role of the left hemisphere which translated to the improvement of learning direction during adaptation to visuomotor control. 15,34,47In the current study, an improvement in visuomotor control was reported as an improvement in the gross manual dexterity (Box and Blocks) test after intervention (Table 2), where the use of the prosthesis and home intervention was assumed to provide closed-loop training.In terms of hemisphere specificity, the results suggest that the intervention had a profound effect on the contralateral (left, dominant) hemisphere of the paediatrics with an affected right limb but on the ipsilateral (left, nondominant) hemisphere of the paediatrics with an affected left limb.This would mean that the intervention provided different benefits based on the handedness of the affected limb and the corresponding dominant or non-dominant hemisphere.Since the prosthesis could be considered to initiate closed-loop training for the affected limb, we could suspect that the home intervention may be more beneficial for ULRD paediatrics with a reduction of the left limb.

Limitations and future considerations
The main limitations of the present study are related to the smaller number of paediatrics with ULRD participating in this study (n = 14), larger age range (6-18 years of age), the inclusion of different reduction levels, including partial carpal (n = 11) and trans-radial (n = 3) reductions, and not separating the ULRD group based on the affected limb, left or right side of the body.To partially control for these limitations, the Control group was age-and sex-matched and utilized a prosthetic simulator equivalent to the prosthesis utilized by the ULRD group.Future studies should include additional coordination tasks in order to connect a specific function to the respective hemisphere as well as resting-state fNIRS measures to measure inter-network communication.In addition, future studies should utilize the side of the body of the affected limb as a covariant as the affected limbs were not separated in this study due to the smaller population size.

Conclusion
We have demonstrated that an 8-week prosthesis home intervention provided benefit to paediatrics with ULRD.The observed behavioural improvements and cortical plasticity may suggest a functional role of the left hemisphere to improve performance as well as the potential embodiment of a prosthetic device in the cerebral cortex after extensive prosthesis training.

Figure 1 TREND
Figure 1 TREND flow diagram.

Figure 2
Figure 2 Experimental design.(A) Description of prostheses and prosthetic simulators.The partial carpal and trans-radial prostheses were utilized by the ULRD group, while the partial carpal and trans-radial simulators were utilized by the Control group.The prosthetic simulators were designed to mimic the control mechanism of the prostheses.The partial carpal simulator allowed the Control group to rest their existing hand on top of the simulator hand, with the wrist in slight extension.A pushing platform placed above the hand allowed wrist active flexion and passive extension to facilitate actuation of the hand.Similarly, the trans-radial simulator incorporates a handle for the Control group to grab and actuate the device by elbow flexion.(B) Participant setup during the Box and Blocks Test.(C) fNIRS head probe with sources and detectors positioned across the sensorimotor cortices.The regions of interest over the sensorimotor cortex are defined as follows: top channels (blue area) = pre-motor cortex (PMC); middle channels (yellow area) = primary motor cortex (M1); bottom channels (red area) = somatosensory cortex (SMC).

Figure 3
Figure 3 Cortical activity during the Box and Block Test.ΔHbO activation maps reflecting T-scores heatmaps for each group and limb.Solid lines are statistically significant contrasts surviving correction for multiple comparisons (q < 0.05).Dashed lines are not statistically significant.ULRD, upper-limb reduction deficiency.

Figure 4
Figure 4 Changes in cortical activity due to intervention.ΔHbO activation maps reflecting post-baseline contrast T-scores for each group and limb performing the Box and Block Test.Solid lines are statistically significant contrasts surviving correction for multiple comparisons (q < 0.05).Dashed lines are not statistically significant.ULRD, upper-limb reduction deficiency.

Table 1 Baseline participant characteristics Characteristics Participants ULRD (n = 14) Control (n = 14)
Data are presented as the number (percentage) of participants.When describing the limbs of each group, the limbs of ULRD group are characterized as affected limb and non-affected limb, while the limbs of the Control group are characterized as non-dominant and dominant limb.The affected limb of ULRD group utilized the prosthesis while the non-dominant limb of the Control group utilized the prosthetic simulator.

Table 2 Average (mean ± SD) number of blocks per minute moved during the box and blocks test
a Significant (P < 0.05) increase as compared to within-group/hand baseline measures.